Dr Peter Smyth, Principal Investigator, Conway Institute
Irish women of child-bearing age are not getting enough iodine in their diet, which could harm the neuropsychological development of their unborn foetus and impact on the intelligence quotient (IQ) of their children and on the incidence of attention deficit and hyperactivity disorder (ADHD).
These preliminary results published recently in the Irish Journal of Medical Science are from a research study carried out by a UCD research team headed by Dr Peter Smyth, principal investigator in UCD Conway Institute of Biomolecular & Biomedical Research and senior lecturer in the UCD School of Medicine & Medical Science along with his UCD colleague, Professor Colm O’Herlihy from the National Maternity Hospital, Holles Street.
The developing foetus does not possess a functioning thyroid gland until 13 – 15 weeks gestation. It relies solely on the presence of maternal thyroid hormones to ensure neuropsychological development. In turn, the availability of these hormones is dependant on an adequate supply of iodine in the diet of the pregnant mother. The research looked at 54 women attending the National Maternity Hospital in the first trimester of their pregnancy as well as measuring the iodine content of diary milk on sale in Dublin at this time.
Smyth and O’Herlihy carried out similar studies in the mid-90’s and the present report shows that iodine intake in the diet of women of child-bearing age seems to have declined in the intervening years. With dietary iodine deficiency representing the single greatest form of preventable brain damage and diminished IQ worldwide, the children of iodine deficient mothers are at risk of not reaching their full intellectual potential.
The results showed that dietary intake of iodine by Irish women is significantly less than the level recommended by the World Health Organisation. This is a greater problem in the summer months when available iodine in food sources such as dairy milk is at its lowest level.
Iodised salt is the primary dietary source of iodine and many countries have introduced systems of either voluntary or mandatory universal salt iodisation (USI). Changing the ingredients of salt to include iodine does not increase usage but improves the dietary quality of the consumer purchase.
However, Ireland and the UK are at the bottom of the USI league table with iodised salt making up only 3.3% of all salt sold. This compares poorly with many of our European neighbours, the United States, Asia and even African countries where between 60-90% of households use iodised salt. As a consequence, the availability of iodine in the Irish diet is entirely opportunistic and based on dietary preference for iodine containing foods such as seafood (shellfish, white deep-water fish) and seaweed kelp.
Commenting on the findings, Dr Smyth observed that while there is as yet no available evidence of widespread underactive thyroid function in the Irish obstetric population, the findings are a cause of concern, which if confirmed by a more comprehensive investigation, may indicate a need to increase the dietary iodine supply to both pregnant women and those of childbearing age. This investigation is ongoing and is supported by the Health Research Board.
